Occlusion of the coronary arteries can decrease blood flow to the extent that a myocardium infarction occurs. This typically occurs due to cholesterol or plaque depositing on the vessel walls and subsequently building up to occlude the vessel. As a result, several minimally invasive procedures such as balloon angioplasty or laser ablation are utilized to reopen or enlarge the lumen of the vessel. A problem with these procedures is that abrasion or dissection of the vessel wall may occur during the therapeutic procedure to reopen or enlarge the lumen of the vessel. As a result, thrombi formation and occlusion of the vessel lumen may also occur.
In addition to balloon angioplasty or laser ablation procedures, a coronary stent is typically positioned in the treated vessel to maintain the patency of the vessel. A problem with the use of a stent is that smooth muscle proliferates or intimal hyperplasia occurs in response to the presence of the stent in the vessel. As a result, restenosis of the vessel typically occurs within a period of six months.
An approach to decreasing smooth muscle proliferation or intimal hyperplasia is the use of a stent with a radioisotope source for irradiating tissue at the stent site. The radioisotope source is contained in the surface coating of the stent or contained in the metal alloy that forms the stent. In use, the stent is embedded into the plaque on a blood vessel wall. A problem with the use of this radioactive stent is that the stent is a permanent implant in the blood vessel. As a result, smooth muscle proliferation or intimal hyperplasia may occur in response to the presence of the stent in the vessel over the entire life of a patient, causing chronic restenosis of the vessel. A limitation of the use of this stent is that the radiation exposure to the stent site is controlled by the half-life of the radioisotope. Once implanted, the radiation dosage of the stent cannot be increased or decreased in response to the changing needs of the patient. Not only are these problems associated with the coronary vessels but are applicable to other parts of the vascular system, such as the occlusion of the femoral or iliac vessels.